This invention relates to a seal ring useful for sealing fluids.
A conventional O-ring made of an electic material is well known as an element for sealing fluids. As shown in FIGS. 1 through 3, an O-ring 30 is accommodated in a circular groove 33 formed on an outer peripheral surface of a shaft member 32. As shown in FIG. 2, when the shaft member 32 is inserted into a cylindrical member 35 in a direction designated by an arrow N, the O-ring 30 is pressed by an inner peripheral surface 36 of the cylindrical member 35 to be deformed. That is because the O-ring 30 is formed so that an outer peripheral portion of the O-ring 30 is larger than the inner peripheral surface 36 of the cylindrical member 35 in diameter. In this case, the O-ring 30 is compressed in a radial direction in the circular groove 33. Thus, a space 38 defined by the inner peripheral surface 36 and the shaft member 32 is sealed by the O-ring 30.
The conventional O-ring 30 is compressed 15% through 20% of the volume thereof when sealing fluid. The more the O-ring 30 is compressed, the more the seal performance of the O-ring 30 is enhanced. As shown in FIG. 3, when inner pressure is applied to the O-ring 30 in a direction designated by an arrow P, the O-ring 30 is moved in an axial direction (for example, upwardly FIG. 3) in the circular groove 33. When a part 30c of the O-ring 30 is pressed into the space 38 between the cylindrical member 35 and the shaft member 32, the insertion load and sliding resistance is increased. As a result, it is difficult to fit the shaft member 32 into the cylindrical member 35 and to disconnect the shaft member 32 from the cylindrical member 35. In this case, however, if the deformation of the O-ring 30 is reduced in order to improve the operational performance, the seal performance becomes incomplete.